The changing epidemiology of serious bacterial infections in young infants.

Background: Management of febrile young infants suspected of having serious bacterial infections has been a challenge for decades. The impact of changes in prenatal screening for Group B Streptococcus and of infant immunizations has received little attention in population-based studies.

Methods: This study analyzed all cultures of blood, urine and cerebrospinal fluid obtained from full-term infants 1 week to 3 months of age, who presented for care at Kaiser Permanente Northern California during a 7-year period utilizing electronic medical records.

Results: A total of 224,553 full-term infants were born during the study period. Of 5396 blood cultures, 129 bacteremic infants were identified (2%). Of 4599 urine cultures, 823 episodes of urinary tract infection (UTI) were documented in 778 infants (17%). Of 1796 CSF cultures, 16 infants had bacterial meningitis (0.9%). The incidence rate of serious bacterial infections (bacteremia, UTI and meningitis) and febrile serious bacterial infections was 3.75 and 3.1/1000 full-term births, respectively. Escherichia coli was the leading cause of bacteremia (78), UTI (719) and bacterial meningitis (7). There were 23 infants with Group B Streptococcus bacteremia including 6 cases of meningitis and no cases of Listeria infection. Nine percentage of infants had multiple sites of infection; 10% of UTIs were associated with bacteremia and 52% of bacteremia was associated with UTI.

Conclusions: Compared with earlier studies, UTIs now are found significantly more often than bacteremia and meningitis with 92% of occult infections associated with UTIs. These data emphasize the importance of an urinalysis in febrile infants.